Considerable progress in understanding the structure and biology of prions as well as the diseases they cause has been made during the past year. Molecular cloning studies have elucidated the genetic origin and structure of the prion protein (PrP). This approach also led to the discovery of the cellular prion protein (PrPC). Ultrastructural studies have shown that prions may exist in at least 3 different states: 1) membrane-bound form, 2) rods, and 3) spheres. Studies on the genetics of scrapie and CJD have shown that at least 2 host genes influence the incubation period. The second gene designated PDI-2 is linked to the prion protein gene. Scrapie is rapidly becoming the most well understood degenerative neurologic disorder. Studies on myelin basic protein (MBP) genes have led to chromosomal assignments in mice and humans, elucidation of the gene structure in mice and sequencing of the first exon from the human MBP gene. During the coming year, studies on the genetics and ultrastructure of scrapie prions will continue. Work on MBP gene structure, therapy and polymorphisms will be performed.